1. Field of the Invention
The field of the invention relates to apparati and methods for monitoring particles in clean environments of the integrated circuit, electronic, pharmaceutical and other industries.
2. Statement of the Problem
The semiconductor and data storage industries are moving away from ballroom cleanrooms with exposed process environments toward enclosed process tools with autonomous air handling systems. Each process tool may be viewed as comprising a mini-environment, in which one or several process functions are performed. A mini-environment-based process tool may contain one or more than one clean-zone, each clean-zone incorporating separate filtration services and product handling systems. Thus, a modern integrated circuit manufacturing plant, commonly known as a fab, typically contains hundreds of smaller, miniaturized mini-environments. Mini-environments exist in a wide range of sizes, a typical size having a volume of 3 mxc3x973 mxc3x973 m. Because the air handling systems of a mini environment are close to the product, extremely isolated contamination events occur. Contamination is often not constant rather it may be a result of a process event. Thus, contamination events may be spatially or chronologically isolated. One of the serious problems of the integrated circuit manufacturing industry, as well as other industries requiring very clean environments, is the detection of these isolated events.
In typical fabrication sequences, front-opening-unified pods (FOUPs) carry wafers to the many mini-environments, robotics transfer wafers from the FOUPs to a manufacturing process zone, and after processing, the wafers return to the FOUPs. Data from mini-environments show that they are not as clean as initially imagined. Consequently, a mini-environment requires particle monitoring, and indirect air handling and compartmentalized nature of the mini-environment necessitates a particle counter with small dimensions and high probability of detecting an isolated particle event.
There are several basic methods known in the art for monitoring a mini-environments. The first is to use a dedicated sensor for each mini-environment to do continuous monitoring. A second technique is to use a multiplexed system, including a stepping manifold system and a single particle detector. With this technique, samples are drawn continuously from numerous mini-environments or from multiple points in a single mini-environment and are measured sequentially in steps a single sample at a time. A third, non-automated method uses a mobile sensor that is moved from one mini-environment to another. The sensor is attached to a xe2x80x9cparticle portxe2x80x9d on the mini-environment.
FIG. 1 shows a diagrammatic sketch of a dedicated sensor system 100 as known in the art. A process tool 102 includes an enclosed gaseous mini-environment 104, which is being monitored for use of a sampling probe 106 which is connected by sampling to 108 to particle detector 110. A dedicated sensor, provides the obvious advantage that it continuously monitors the sampling zone of the sample probe, capturing brief intermittent events. A serious disadvantage, however, is that the sampling zone of a dedicated sensor is relatively small, typically having a footprint less than one square foot. A dedicated sensor, therefore, provides limited spatial coverage, detecting particles only in the sampling zone, and not in the other locations of the mini-environment. For example, a diagram of a process tool 202 is depicted in FIG. 2 containing a mini-environment 204 and four process functions 206, 208, 210, 212. The movement of a semiconductor wafer 214 through process tool 202 includes travel through zones designated by dashed area 220, including the liquid environments of process functions 206, 208, 210. Movement through the process tool 202 also includes travel through a gaseous clean zones along the path designated by arrows 230. A 12-inch wafer has a surface area of 0.8 sq. ft. If the exposed path through the gaseous mini-environment of the process tool is 24 feet, then the effective exposed area for the wafer is 19 sq. ft. A particle contamination event is generally localized to an area corresponding to 1 square foot or less. Thus, a dedicated sensor located at a single point along the 24-foot exposed process path 230 would detect a contamination event only if the event occurred within several inches of the location of the sampling probe. It is, however, economically and sometimes physically impractical to provides a large number of dedicated sampling probes and corresponding expensive particle counters to monitor continuously the entire process path of a process tool.
In a multiplexed monitoring system, a number of sampling probes are connected to a multiplexed stepping manifold. A diagrammatic sketch of the multiplexed monitoring system 300 is depicted in FIG. 3. Typically, fluid is drawn from each sample point 302 continuously through the multiplexing stepping manifold 310 by pump 350. In sequence, the manifold controller 312 selects a single sample 320 that is tested by the particle detector 330, while all other fluid flow from the unselected samples is discarded in the exhaust system 340. A multiplexed, stepping manifold system 300 allows monitoring of many locations using a single particle detector. A multiplexed system has a disadvantage, however, that a contamination event may go undetected for a relatively long time until the sample from the probe location reaches its turn in the multiplexing sequence. Indeed, a brief or intermittent contamination event may go completely undetected if its occurrence does not coincide with the timing of the multiplexing sequence. In a variation, referred to as a mixed-fluid manifold technique, two particle detectors are connected to each stepping manifold. A single sample is selected by the manifold and sent to one particle detector, as in a basic system, while the samples from all the other sample probes are combined and sent as a mixture to the second particle detector. In this manner, each sample probe location is monitored individually in sequence, while a combined mixed-fluid stream of all of the remaining samples is monitored continuously. This technique is expensive, however, because it requires two particle detectors and an expensive multiplexed stepping manifold with extra controls.
Conventional monitoring systems using stepping manifolds to monitor a mini-environment at a number of sample points typically draw a large volume of the air, sometimes greater than 1 cubic foot, from each sample point. This may adversely affect the whole fluid environment. The tubing leading to the probes takes up limited space in the process tool. When there are many sampling points to be monitored, it may be impossible to provide access for tubing to all of the sampling probes. Particles in the tubing, especially aerosol particles, may settle in the tubing, leading to false negative or low measurements and to clogging of the tubing. The stepping manifolds used in conventional techniques typically way on the order of 20 pounds, and occupy a large volume of space, having a diameter of a foot or more.
The mobile system has the advantage of having the lowest capital cost. But, it has the disadvantage of increased manpower costs and has a very low duty cycle.
The problems described above with respect to monitoring clean gaseous environments are also encountered in regard to maintaining clean liquid environments.
The integrated circuit manufacturing industry, as well as other industries requiring clean environments, needs a particle monitoring system that monitors and detects contamination events in a clean environment, providing good spatial coverage without significant gaps in time, in a manner that is economically and physically feasible.
The invention described in this specification provides an ensemble manifold, a system and a method that alleviate the problems described above.
An ensemble manifold in accordance with the invention combines all of the fluid samples collected in a clean environment and provides this ensemble flow to a particle detector. An ensemble manifold comprises: a plurality of sample ports; a delivery port adapted for fluidic connection to a particle detector; and a flow junction located between the sample ports and the delivery port, in which fluids flowing through the sample ports are combined.
In another aspect, an ensemble manifold comprises: a plurality of sample ports; a flow cell of a particle detector, in which fluids flowing through the sample ports are combined; and an outlet port.
A system in accordance with the invention for detecting particles in a clean environment comprises: an ensemble manifold having a plurality of sample ports and a delivery port; a plurality of fluid sources located in the clean environment, each of the fluid sources fluidically connected to one of the sample ports; a particle detector, the particle detector fluidically connected to the delivery port of the ensemble manifold. An embodiment of a system in accordance with the invention comprises a plurality of sampling probes in fluidic contact with the fluid sources, each sampling probe fluidically connected to one of the sample ports. Preferably, the sampling probes are isokinetic sampling probes. Typically, the clean environment is a mini-environment of a semiconductor wafer process tool. Fluid samples may be drawn from the clean environment into an ensemble manifold using house vacuum or vacuum pump or other suitable means. In a preferred embodiment, a system comprises a plurality of sample tubes, one end of each sample tube attached to one of the sampling probes, and the other end of the sample tube attached to one of the sample ports. Preferably an ensemble manifold comprises a special manifold adaptation designed for direct mounting of the ensemble manifold onto a selected particle detector. In another embodiment, a system may comprise a delivery tube for connecting the outlet (delivery port) or the ensemble manifold to the particle detector. The delivery tube has two ends, one end of the delivery tube attached to the delivery port of the ensemble manifold, and the other end of the delivery tube attached to the particle detector.
A method in accordance with the invention for detecting particles in a clean environment comprises steps of: continuously simultaneously drawing a plurality of fluid samples at a plurality of sample points in the clean environment; continuously combining the plurality of the fluid samples into a combined fluid stream (ensemble flow); continuously flowing the combined fluid stream into a particle detector; and then monitoring the combined fluid stream with a particle detector. Typically, each of the fluid samples is drawn through one of a plurality of sampling probes located at the plurality of sampling points, each of the sampling probes fluidically connected to one of the sample ports. Preferably, the drawing of fluid samples is conducted isokinetically. For this reason, the sampling probes preferably are isokinetic sampling probes. Preferably, the clean environment is a mini-environment of a semiconductor wafer process tool. A method in accordance with the invention is useful when the fluid samples comprise gaseous fluid and the particles are aerosol particles. A method in accordance with the invention is also useful when the fluid samples comprise liquid fluid.